1. Field of the Invention
The present invention relates generally to sealing a space between adjacent plates or ledges. In particular, the invention relates to sealing the space between an annular flange on a nuclear reactor vessel and a surrounding ledge of a refueling canal to provide a temporary water barrier between the refueling canal and the reactor vessel during refueling operations.
2. Description of the Related Art
The conditions giving rise to the problems solved by the present invention are commonly found in nuclear reactor power plants. In particular, the refueling process in pressurized water reactors must be performed under approximately 25 feet of water in a refueling canal above the reactor vessel, while the reactor vessel cavity under the canal must be maintained dry. During normal power operation the refueling canal is dry and, with the vessel cavity, forms a single large enclosure. Typically, a portion of the floor of the refueling canal forms a ledge opposite a flange attached to the upper portion of the reactor vessel. The ledge and flange provide sealing surfaces on which prior art canal sealing interfaces were effected.
Conventional refueling pool seals are of two general types: temporary and permanent. Temporary seals typically comprise a ring plate having an outside diameter of about 25 feet and a width of from 1 to 3 feet. Compression elastomer seals carried on the underside of the ring plate rested on the flange and ledge. The ring plate was bolted down to the flange and ledge to compress the seals and form a watertight fit.
Another temporary seal was developed having a rigid plate bridging the annular space to be sealed, and a pair of inflatable seals positioned between the reactor vessel flange and the rigid plate, and between the rigid plate and the ledge of the refueling canal. This arrangement is disclosed, for example, in U.S. Pat. No. 4,908,179, which issued to Robert H. Brookins on Mar. 13, 1990, and was assigned to Combustion Engineering, Inc., assignee of the present application. These temporary seal arrangements are relatively difficult and time consuming to install, thereby resulting in an undesired amount of occupational radiation exposure.
Permanent seal arrangements have been developed that remain in place during normal power operation and during refueling. An example of a permanent refueling pool seal is disclosed in U.S. Pat. No. 5,102,612, which issued to Michael S. McDonald et al. on Apr. 7, 1992, and was assigned to Combustion Engineering, Inc., assignee of the present application. This permanent seal comprises annular deck sections supported on spaced ribs around the annular space to be sealed. The inside and outside diameters of the deck sections are welded to flexible membranes to make a watertight seal between the reactor vessel flange and the ledge of the refueling pool cavity. The deck sections include openings with removable seal covers. These openings provide reactor cavity cooling air flow and an access path to the reactor vessel cavity and external core detectors when the seal covers are removed. However, removal of the seal covers to establish a ventilation path from the reactor cavity during plant operation is time consuming, thereby resulting in an undesired amount of occupational radiation exposure.